Page and folder security is broken

The custom security feature for both pages and folders appears to be broken. I added several new users to a secured folder last night. Everything seemed to work fine, but I received an email this morning from one of the users saying that they didn't have access. I logged in and I couldn't see the user names of any users (though there lines in the user table, just no names) and there were not enough lines for the new users I added to be included. I deleted all of the blank lines and added all of the users again. When I clicked save they all disappeared. I tried this several times in the folder's security with the same result and the tried to use the page security instead, again same result. I am the administrator and the wiki is 2.0 and upgraded to gold. Please help!